a. Field of the Invention
The present invention relates to a developer for use in electrostatic photography, and it particularly relates to a liquid developer for use in electrostatic photography which demonstrates a superb effect in transfer of image.
B. Description of the Prior Art
As the method of developing an electrostatic latent image formed on the electrophotographic copying material, electrostatic recording material, etc., there are generally known the dry-developing method and wet-developing method. Further, the developing method is classified into the transfer process and the direct process by the difference of the process for obtaining the final copies. Accordingly, it is theoretically possible to employ either the dry-developing method or wet-developing method for both the transfer process and direct process. The wet-developing method is superior to the dry-developing method in that it renders a copied image with less edge effect and a high resolving power. Meanwhile, the transfer process renders it possible to form a copied image on an ordinary paper film and other materials not provided with a photoconductive layer, so that it has an advantage that the resulting copies are easy to handle as compared with the case of the direct process.
However, the transfer process has hitherto employed the dry-developing method, and application of the wet-developing method to the transfer process has scarcely been tried. The main reason for this is as follows. According to the dry-developing method, inasmuch as the toner for dry process to serve as the developer is a dry powder and not possessed of tackiness, the image formed on the photoconductive layer is easy to transfer and the residual image on the photoconductive layer after transfer is also easy to remove, while, according to the wet-developing method, inasmuch as the developer for use therein is one prepared by dispersing the toner for wet process in an insulating carrier liquid, the toner image formed on the photoconductive layer is possessed of tackiness, so that transfer cannot be performed sufficiently and the residual image is hard to remove.
As the known developer for use in electrophotography, there is, for instance, a developer disclosed in Japanese patent publication No. 11069/1966. The toner employed for this developer has a comparatively good transferability, but as the electric charge of said toner is indistinct, the concentration of the image becomes insufficient, there is brought about a stained ground, and further the transferred toner is poor in fixability and unusable for wet-process transfer.